Pulled the cylinders top of piston is melted along with the grove on the top that holds the rings on the MAG side scuffing on exhaust and intake

 

Carb boots are due for replacement but did not cause this
Carbs are clean with no signs of water
360 mains

Any thoughts ?

 

Jon, could this be the result of running hot mids in extreme cold? Or from a gas container holding older gas?

 

@Daag44 the temp was from -5 to around +1

Gas was a few weeks old and Reg

Talking to my friend and he said he bought the sled with 1000KM on it when it was a few years old (lets say it was 2011), his first run on a snow covered lake and the machine shut off, waited drove it back to his house and left it outside to cool down. went to put back into garage carbides dug in he hit reverse and the motor locked up. My thoughts is this was jetted LEAN from the factory it stuck the first time eating the piston got it going on one cylinder drove it home when he shifted into reverse the piston with its new Clarence turned in the cylinder due to the change in the direction oF the motor and caught a transfer port and locked it up

Moving on he got the motor rebuilt light use no issues

2022 this sled has only been driven 2000 km from rebuild (total of 3000 km on it now)

 

New clearance as in the pistons were given added clearance for the last build? Or do you mean ring clearance? In the case of a plug melted electrode I am thinking detonation. The picture of the piston isn't clear enough to see. Can you explain how it looks? Was the exhaust side melted? Did the ring stick in between the exhaust ports? What kind of oil was used, the fancy brand that says they are as good or better than XPS? I think the failure originated on the lake and loosened the ring locating pin when the ring stuck in the groove on the exhaust side. Do you have an idea of the rpm and load when this happened? Whoever has an EGT in the y-pipe or tuned pipe or muffler can look for the precarious rpm range and load where the pistons get really hot.

 

Lol new clearance as the piston scored up the cylinder allowing for slop side to side movement of the skirt then caught in the cylinder port when put into R ? ( BUT THIS was the first time it blew up)

I think the issue was not FIXED from the first time and the lean jetting happend again. Piston top is black with a melted crator ontop and the ring grove is gone on ex side exposing the ring. Ex side skirt is bad intake has marking on it also

BRP mineral oil

No idea on RPM at time of failure probably balls as he was trying to catch me

 

iston top is black with a melted crator ontop and the ring grove is gone on ex side exposing the ring. Ex side skirt is bad intake has marking on it also

That's detonation which puts gasoline at the top of the list. I also wonder if the exhaust valves are opening evenly.

 

Could it bad crank seal on the MAG side.
How does the PTO side look like.
Could it be icing in the carb while running on the lake, anything non OEM in the intake track or have been removed from it (foam filter).

This is just me thinking out loud, I dont need an answer.

 

@alainm thanks for the response

Hummmm bad crank seal Not sure

PTO side is fine (going to re-ring it)
Dont think it was ice in the carb

All stock machine

 

When the problem is recurring you need to look at what hasn't been touched in a while.
Try emptying the fuel tank and see for a accumulation of water mixed with ethanol, it is easy to see if you put it into a glass jar.

On my 2002 380 fan I was having a similar situation and the second time it happened I pulled the fuel hose from the pump and the gas was orange, where did the orange come from no idea, plastic fuel tank plastic fuel hoses and aluminum fuel pump would not cause this and all my fuel is bought at reputable high volume gas stations, all I could see is water absorption over time in the gas.

 

i checked last night and the MAG side RAVE valve was sticky

 

The E-TEC has them linked so that one cannot open without the other, and to monitor valve position. This is just to say how important it is for both valves to fully open. XPS Mineral and enough of it will help keep away the sticky valve gremlins.

 

Did you say Mineral or did you mean synthetic, I run mineral only in fan's any thing with exhaust vales I run full synthetic.

 

Long please @Daag44

 

For the truncated version, the quality of the build raises many question with how the oil is retained on the cylinder wall and how it migrates. Then add the first 50 miles out of storage is where things are likely to happen. Something to think about, a piston that runs hotter and uses the synthetic, or one that is cooler and uses mineral? The same exercise can be used with cylinder finish and blowby. I often wonder the effect of the oil from the blowby with a new ring in a used bore that takes thousands of miles to fully seat, versus a new ring in a properly honed bore that seats within a few tanks.

 

Longish for me.

 

What model year is this sled please?

 

its a 2008 GTX 500ss

 

So, my current rebuild, the mechanic said the sleeves were in great condition and didn't require boring...?

 

The problem is we have no way to know without measuring it. Either take a chance, or since you are in the USA you can ask MCB if they are willing to take a look. At this point they are the only ones that I am aware of who have an actual standard, other than of course BRP. And for your Mach Z, that is the only place I would go.

 

...same engine as this thread, correct?

2004 MXZ 500SS melted piston

We switched from Polaris to Skidoo this season. I got a 2005 MachZ. This is about my wife's sled, 500SS We rode about 70 miles. This was our first ride with this sled. It backed off the trailer OK starting the trip. It failed going into reverse while loading with the engine warm (hot?) at the...

www.dootalk.com

 

Yes, and what works for your 500SS will work for your 1000 SDI, except of course for the cylinder finish.

 

As an FYI, the OP (Jon) is the one who figured out the cause of the wiring harness on the 600 SDI getting soaked and causing the splices to corrode, assumingly from road salt. DooTalk is in dept for the work he has done and shared on the forum. Time to pay it back

 

Guys learning things every day here, thanks.

Too bad conditions had gone to sh!t so fast this year, hopefully this snow we just got hear in QC will get us back to a few more weeks of sledding.

 

Thanks for the replies and information

This is where we are with uncle ricks sled

going to bore the melted side 1st over OEM piston ordered
STD rings for non melted side
Clean rave valves as the melted side was very sticky (ordered Rave gaskets)
two new exhaust gaskets
two new carb boots from royal distributing ($39 each)
New base gasket
drain the gas tank
inspect and clean the carbs (although they are spotless not)

I am going to order new circlips and a bearing for the melted side (OEM)

still unsure on jetting this
it has 360 mains now

My thought is go up to 370 and move the needle up and turn up the oil pump

i am no expert on jetting or anything for that matter lol

would really like some input on things i can do to keep this from happening again

 

I am no expert on jetting or anything
would really like some input on things i can do to keep this from happening again

Did you get it running? I'm convinced this was an engineering/Product Development short-sight.

Looking at this maybe?

Ski Doo 600HO/700 & 500SS Big Bore Kits

Ski Doo 600HO/700 & 500SS Big Bore Kits Ski Doo The Series III 700 Twin is BY FAR the most impressive 700 twin on the market!! However;as you read above (hopefully), it is plagued by poor heat conduction from the piston to the cylinder wall via the ring. RK Tek tried various combinations...

www.2strokeheads.com

 

I'm thinking similar for my wife's. From what I've read, the fuel is the lube in these things.
Once they get hot, that is when they go past and detonate because the hot spots in the engine ignite the fuel before the spark plug fires - before the timing

Try to keep the temp down below whatever that magical number is. The extra fuel is also a coolant carrying heat out the exhaust. When it burns more clean / lean, and less heat is carried away creating even more heat in the combustion chamber.

 

The magical/maximum engine/coolant temperature that you referred to is somewhere around 170F - for a maximum. It will not self destruct above this temperature, but from there on the risk increases much like a parabolic curve. And each situation is different. Say it reaches 200F, what is the condition? Many E-TEC owners let their sleds warm up and count on the ECM to shut the engine which happens after idling for 5 seconds @ 204F. But when riding the same E-TEC and it reaches 185F, then it is considered an overheat and the engine is cut down on power to 5,500 rpm. In other words, there is a difference in overheat when riding under load compared to when it is idling.

When I see posts that a Ski-Doo was towing an Arctic Cat or Polaris or Yamaha, I get the humour, but it is so hard on the transmission and the engine that I find the humour at a loss.

On a side note, I think that you should continue to push the 500SS thread that you started. I am not worried about the OP (Original Poster) jon@nlxdirect.com because he brought an illuminating explanation to a common a SDI wiring problem. I am not worried about you either, mostly because you had the balls to post on a public forum. I am just saying to keep pushing, because these subjects do not often go far enough to reach maturity. The off-season provides more time to think things through. I think you started a real cool thread on the 500SS that begs to dig further.

2004 MXZ 500SS melted piston

 

They appear to overheat and cause detonation and melted pistons in these engines.

 

Fortunately a single ring doesn't cause detonation.

 

...after coming back and re-reading what I wrote and your reply, I was referring to the head and possibly the coolant volume/speed of coolant flow?

 

I did this after a preventative rebuild melted down before breaking in.

I had a friend pressure test my 500ss in chassis. No air coming or going from crankseal. Reeds y pipe rave sealed up good this left the carbs slides.
I put the thickest base gasket I could I.
Carbs up jetted 2 sizes. Piolts 1 size. Moved the needle clip down.
Switched to Br10ecs.
Premix 40:1 and oil injection.

The sled made more power with these settings (added pin weight) and I can confidently park the throttle on the bar what a feeling.

I know some won't agree with these and they are band aids but they rebuilt my trust in my sled.. that's worth something.

 

The sled made more power with these settings (added pin weight) and I can confidently park the throttle on the bar what a feeling.

I know some won't agree with these and they are band aids but they rebuilt my trust in my sled.. that's worth something.

If you can make good power with those settings, seriously all the power to you! From your profile I suspect that you ride Iqaluit, NU, and the temperature is colder then where I ride. I imagine the jetting-up was appropriate. A little less compression with a thicker base gasket is not a big power loss. I am guessing that by now you have figured out the best engine mod for the buck is a running engine.

Good compression from the ring(s) with a thicker base gasket has more power than a thinner base gasket having poor compression from excess blowby. A thicker base gasket also holds the advantage of running 87 in remote regions where the gasoline tends to see longer storage which looses RVP and octane.